The present invention relates to the field of hydrocarbon upgrading processes. In another aspect, the invention relates to the disproportionation of isoparaffinic hydrocarbons.
Disproportionation of hydrocarbons, as referred to herein, involves the conversion of hydrocarbons having x number of carbon atoms per molecule to hydrocarbons having xxe2x88x921 number of carbon atoms per molecule and to hydrocarbons having x+1 number of carbon atoms per molecule. The production of high octane-rating gasoline is desirable in order to meet the octane specifications for gasoline fuel. One way in which high octane gasoline can be produced is by the disproportionation of hydrocarbons to produce higher octane-rating gasoline, as described in U.S. Pat. Nos. 3,763,032 and 3,767,565. However, as gasoline fuel specifications become more stringent concerning sulfur content, aromatic content and Reid vapor pressure (xe2x80x9cRVPxe2x80x9d, defined as the vapor pressure of a hydrocarbon at 100xc2x0 F. (37.8xc2x0 C.) in pounds per square inch absolute and measured using ASTM test method D-323), the demand for diesel fuel could significantly increase should the motor vehicle industry increase the production of motor vehicles running on diesel fuel. Therefore, development of a process to convert a hydrocarbon feedstock comprising gasoline range hydrocarbons, containing paraffins and isoparaffins, to a gasoline range stream with enhanced octane-rating over that of the hydrocarbon feedstock and to a diesel range material having an enhanced cetane number over that of the hydrocarbon feedstock would be a significant contribution to the art and to the economy.
It is an object of the present invention to provide a novel process for disproportionating isoparaffins and paraffins to produce diesel fuel range hydrocarbons.
It is still another object of the present invention to provide a novel process for disproportionating isoparaffins and paraffins to produce gasoline range hydrocarbons.
It is yet another object of the present invention to provide a novel process for disproportionating isoparaffins and paraffins to produce diesel fuel range hydrocarbons having a higher cetane number than the isoparaffins and paraffins and gasoline range hydrocarbons having a higher octane-rating than the isoparaffins and paraffins.
In accordance with the present invention, a process has been found for disproportionating hydrocarbons comprising the steps of:
contacting a hydrocarbon feedstock comprising isoparaffins and paraffins with a disproportionation catalyst, in the presence of at least one initiator, to thereby produce a product stream comprising a diesel range material; and
recovering the diesel range material from the product stream.
In one embodiment, the cetane number of the diesel range material is higher than the cetane number of the hydrocarbon feedstock.
In another embodiment, at least a portion of a hydrocarbon feedstock comprising isoparaffins and paraffins is converted to a gasoline range material and a diesel range material in a process comprising the steps of:
contacting the hydrocarbon feedstock with a disproportionation catalyst, in the presence of at least one initiator, to thereby produce the gasoline range material and the diesel range material having a higher cetane number than the hydrocarbon feedstock, wherein the combined volume of the gasoline range material produced and the diesel range material produced is greater than the volume of the hydrocarbon feedstock;
recovering the gasoline range material; and
recovering the diesel range material.
In still another embodiment, the octane-rating of the gasoline range material is higher than the octane-rating of the hydrocarbon feedstock.
Other objects and advantages will become apparent from the detailed description and the appended claims.
The catalyst useful in the present invention can be any disproportionation catalyst suitable for disproportionating isoparaffins and paraffins. Preferably, the disproportionation catalyst is acidic, and most preferably, is an acid catalyst. Examples of suitable acid catalysts include, but are not limited to, hydrofluoric acid; sulfuric acid; polyfluoroalkyl sulfonic acids, either neat or supported on a solid; perfluoroalkyl sulfonic acids, either neat or supported on a solid; inorganic metal fluorides (such as, for example boron trifluoride) in the presence of hydrofluoric acid; zeolites (such as, for example MCM-36); alumina; aluminosilicates; and zirconia-based solid acids (such as sulfated or tungstated zirconia). The most preferred acid catalyst useful as the disproportionation catalyst is hydrofluoric acid.
The process of this invention involves disproportionating isoparaffins and paraffins. A hydrocarbon feedstock comprising, consisting essentially of, or consisting of isoparaffins and paraffins is introduced or charged, in the presence of at least one initiator, to a reaction zone containing a disproportionation catalyst operated under reaction conditions for disproportionating isoparaffins and paraffins.
Preferably, the hydrocarbon feedstock comprises isoparaffins and paraffins having the formula CnH2n+2 wherein n is an integer greater than 3; preferably greater than 4; and most preferably greater than 8 (that is, the hydrocarbon feedstock most preferably comprises isoparaffins and paraffins, each having greater than 8 carbon atoms per molecule). In addition, the hydrocarbon feedstock can be an alkylation product from an alkylation unit or the heavy alkylate portion of the alkylate product, the heavy alkylate portion comprising primarily C9+ hydrocarbons.
The at least one initiator can be any initiator effective at initiating the disproportionation of isoparaffins and paraffins. More particularly, the initiator useful in the present invention can be selected from the group consisting of at least one olefin, at least one compound of the formula CnH2n+1X, wherein n is an integer and wherein X is a leaving group capable of leaving under disproportionation conditions to form a carbocation intermediate, and combinations of any two or more thereof.
The at least one olefin of the at least one initiator can be selected from the group consisting of ethylene, propylene, butylene, pentene, isopentene and combinations of any two or more thereof.
The X in the compound can be selected from the group consisting of fluorine, chlorine, bromine, iodine, hydroxide ion, and combinations of any two or more thereof The most preferred initiator is an olefin.
The weight ratio of the hydrocarbon feedstock to the at least one initiator can be any ratio effective for disproportionating the hydrocarbon feedstock. Preferably, the weight ratio of the hydrocarbon feedstock to the at least one initiator is in the range of from about 1:1 to about 100,000:1; more preferably from about 10:1 to about 1,000:1; and most preferably from 20:1 to 100:1.
The disproportionation reaction can take place as a batch process step or, preferably, as a continuous process step. In the latter operation, a solid catalyst bed or a moving catalyst bed or a fluidized catalyst bed or a continuous stirred tank reactor can be employed. Any of these operational modes have advantages and disadvantages, and those skilled in the art can select the one most suitable for a particular feed and catalyst.
With the use of liquid catalysts, such as hydrofluoric acid (with and without boron trifluoride) and sulfuric acid, the contact time of the hydrocarbon feedstock with the catalyst is preferably in the range of from about 5 seconds to about 1 hour; more preferably from about 10 seconds to about 30 minutes; and most preferably from 30 seconds to 30 minutes.
With the use of a solid catalyst, such as, but not limited to, polyfluoroalkyl sulfonic acids; perfluoroalkyl sulfonic acids; zeolites; alumina; aluminosilicates; and zirconia-based solid acids, the flow rate at which the hydrocarbon feedstock is charged to the disproportionation reactor is such as to provide a weight hourly space velocity (xe2x80x9cWHSVxe2x80x9d, defined as the pounds/hour of feed to the reaction zone divided by the total pounds of catalyst contained within the reaction zone) in the range of from about 0.01 hours to about 1000 hrxe2x88x921; preferably from about 0.25 hourxe2x88x921 to about 250 hourxe2x88x921 and most preferably from 0.5 hourxe2x88x921 to 100 hourxe2x88x921.
The reaction temperature can be in the range of from about 50xc2x0 F. to about 200xc2x0 F.; preferably from about 90xc2x0 F. to about 180xc2x0 F.; and most preferably from 110xc2x0 F. to 160xc2x0 F. The pressure of the reactor can be in the range of from about 50 psig to about 1000 psig; preferably from about 75 psig to about 500 psig; and most preferably from 100 psig to 250 psig.
The product stream from the disproportionation reactor comprises isoparaffins and paraffins having the formulas Cnxe2x88x921H2n, and Cn+1H2n+4 (which are disproportionation products of a hydrocarbon having the formula CnH2n+2). The isoparaffins and paraffins of the product stream, resulting from the disproportionation, are generally less isomerized than the isoparaffins of the hydrocarbon feedstock. The terms xe2x80x9cisomerizedxe2x80x9d and xe2x80x9cisomerxe2x80x9d, as used herein, are defined as the degree of branching of a molecule. For instance, per this definition, 2,4 dimethylpentane: 
is more highly branched, and thus more isomerized, than 2 methylhexane: 
which is more highly branched, and thus more isomerized, than heptane:
CH3xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94CH3;
while each of these contain the exact same number of carbon and hydrogen atoms.
More particularly, the product stream comprises a diesel range material comprising at least one hydrocarbon having greater than 8 carbon atoms per molecule and a gasoline range material comprising at least one hydrocarbon having less than 9 carbon atoms per molecule.
The combined volume of the gasoline range material produced and the diesel range material produced is preferably greater than the volume of the hydrocarbon feedstock.
The product stream can be separated into the diesel range material and the gasoline range material by any method known for separating hydrocarbons, such as a distillation unit.
The diesel range material has a cetane number, as determined using ASTM test method D613.65, which is higher than the cetane number of the hydrocarbon feedstock. The cetane number of the hydrocarbon feedstock is typically less than 25, more typically less than 24, and most typically less than 23. Preferably, the product diesel range material has a cetane number greater than about 25; more preferably greater than about 28; and most preferably greater than 30.
The product gasoline range material preferably has in the range of from 5 to 8 carbon atoms per molecule. The octane rating of the product gasoline range material is preferably higher than the octane-rating of the hydrocarbon feedstock.
Octane-rating is defined as (RON+MON)/2. RON (research octane number), as used herein, refers to the octane number of a hydrocarbon stream as determined using the ASTM D-2699 method. MON (motor octane number), as used herein, refers to the octane number of a hydrocarbon stream as determined using the ASTM D-2700 method.
The octane-rating of the hydrocarbon feedstock is typically less than about 78, more typically less than about 76, and most typically less than 74. Preferably, the octane-rating of the product gasoline range material is greater than about 78; more preferably greater than about 79; and most preferably greater than 80.
In another embodiment, an i-C5 stream comprising isopentane can be recovered from the product stream before separation of the product stream into the gasoline range material and diesel range material; or from the gasoline range material after separation of the gasoline range material and diesel range material from the product stream. The recovered i-C5 stream can be contacted with the disproportionation catalyst in the disproportionation reactor along with the hydrocarbon feedstock. This leads to the production of more isobutane, an alkylation unit feedstock; more C6 hydrocarbons, a desirable gasoline component; and a lower level of produced isopentane, which is desirable due to the relatively high RVP (reid vapor pressure) of isopentane and gasoline specifications which limit the level of RVP.